Process and material for extracting dissolved radioactive ions from liquids

ABSTRACT

MECROCRYSTALLINE, DIFFICULTLY SOLUBLE SALTS, WHICH ARE ISOTOPIC WITH RADIOACTIVE IONS, ARE FORMED BY PRECIPITATION ON THE SURFACE OF A SUPPORT IN AN AGITATED LIQUID SUSPENSION OF THE SUPPORT. A LIQUID IN WHICH SAID RADIOACTIVE IONS ARE DISSOLVED IN PASSED THROUGH A COLUMN AND CONTACTED IN SAID COLUMN WITH SAID SALTS BONDED TO THE SURFACE OF THE SUPPORT. THIS RESULTS IN AN ISOTOPIC EXCHANGE BETWEEN SAID SALTS AND IONS.

United States Patent Oifice 3,563,890 PROCESS AND MATERIAL FOR EXTRACTHN'G DISSOLVED RADIOACTIVE IONS FROM LIQUIDS Horst Willi Perl, Walter Fritz Rittner, and Oskar Max Glemser, Goettingen, Germany, assignors to Sartorius- Membranfilter G.rn.b.H., Goettingen, Germany No Drawing. Filed July 10, 1967, Ser. No. 651,977 Claims priority, application Germany, July 11, 1966, S 104,735 Int. (ll. Bllld 15/04 U.S. Cl. Z-38 6 Claims ABSTRACT OF THE DISCLOSURE Microcrystalline, difficultly soluble salts, which are isotopic with radioactive ions, are formed by precipitation on the surface of a support in an agitated liquid suspension of the support. A liquid in which said radioactive ions are dissolved is passed through a column and contacted in said column with said salts bonded to the surface of the support. This results in an isotopic exchange between said salts and ions.

In accordance with Section 34 of the First Order for the Protection From Radiation dated June 30, 1960 (Bundesgesetzblatt 1., page 430), it is prohibited in the Federal Republic of Germany to discharge radioactive liquids into the public sewage system if their activity per unit of volume is above a permissible limit. For this reason, the liquids must be stored until their radioactivity has dropped below the permissible limit or the liquids must be decontaminated before they are discharged. The latter practice will be necessary or preferable when the liquids become available in large quantities or when it is not possible to permit in liquids which become continuously available a decay of the radioactivity below the permissible level.

Known process of decontaminating radioactive liquids will be listed hereinafter (1) It is known from conventional processes for treating sewage that impurities can be absorbed by sludge, pumice, slag and other materials having a large surface. Similar installations have been used for a partial decontamination of waste solutions having a slight radioactivity.

(2) More significant are adsorptive coprecipitations on bulky substances having a large surface, such as MnO(OH) Al(OH) Fe(OH) as well as sulfides and sulfates.

(3) Unless salt impurities are present in excessive quantities, radioactive sewage can be purified by an ion exchange.

(4) Distillation has been used in most cases for decontaminating solutions of high activity in small volumes and enables a reduction in radioactivity by a factor of 10 All processes mentioned above are highly expensive and involve high costs. In connection with (1) and (2) it must be borne in mind that filtration results in a radio active product which is solid but has still a fairly large bulk. Organic ion exchangers which have been laden with radioactive ions may be converted into a very small volume of ash but have only a restricted capacity, which limits their use in waters which are contaminated with relatively large proportions of inactive salts.

In the process according to the invention, the known effect of a heterogeneous isotopic exchange is used for decontaminating radioactive solutions in that microcrys- 1 B. Lindner, Kernund Radiochemie, SpringenVerlag 1961.

3,563,899 Patented Feb. 16, 1971 talline, difiicultly soluble salts are produced on a support, which salts are isotopic with the dissolved ions to be exchanged, and the thus impregnated support is charged into a column and is caused to be flown through by the liquids to be decontaminated so that a rapid decontamination i effected.

In a heterogeneous liquid-solid system, the ions of the crystal lattice of a precipitate are in a state of thermodynamic equilibrium with the isotopic ions which are present in a solution (liquid phase) in contact with the precipitate (solid phase). There is a continuous exchange of ions. Ions which were originally in solution occupy sites in the lattice of the solid phase and ions of the lattice are dissolved.

This effect has been known for many years 2 3 4 and has been the subject of a large number of investigations. It was believed that this phenomenon can be used for a determination of surfaces of ionic crystals 4 5 On the other hand it was possible to investigate the nature of the surface of ionic crystals which are in contact with a solution More recently, Lieser and those who worked with him 9- 12 have mainly endeavored to clarify the kinetics of the heterogeneous isotopic exchange and its dependence on various parameters. Finally, specific radiochemical processes should be mentioned which have been developed on the basis of the effect of the heterogeneous isotopic exchange 13 The observations made in these numerous experiments have shown that the velocity of the heterogeneous isotopic exchange depends on the surface reaction at the crystal-solution interface rather than on the rate of the diffusion of the ions in the solution. The isotopic exchange on the surface is followed by the recrystallization of the solid phase under the influence of the solution. This reportance for the rate of the heterogeneous isotopic exchange.

In the experiments carried out mainly by batch processes, the systems exhibited half-exchange periods of minutes to several hours. Only conditions such as have recently been described by Rai 16 enable a complete exchange with very low activities and amounts of liquid F. Paueth, Chem. 101, 445 (1922).

F. Paneth, Radio-Elements or Indications, McGraw Hill Book 00., 1928, pages 55-79.

4 C. Wahl and N, A, Bonner, Radioactivity Applied to Chemistry, John Wiley and Sons, Inc., New York 1951 gg sin ieton and J. Sprinks Canad. J. Res. Sect, 1127, 238 8R. Stow and .T. Springs, J. Chem. Physics, 17, 744 (1949 43, 871 1939).

O. Hahn, 0. Entacker, and N. Feichtinger, Z. angew. Chem, 42 871 (1930).

14 K. Fritze. T. J. Kennett, W. V, Prestwich, Ganad. J. Phys, 39 662 (1901).

(1961 1I.) R. Johnson, E. Eichler et 211., Phys, Rev., 122, 1546 R, S, Rai et al., Radiochim. Aeta 5. 30 (1966).

Where the contact times are of an order of seconds. In this process, the radioactive solution is sucked through a thin layer of a difiicultly soluble salt which has just been precipitated.

The process according to the invention enables a rapid and complete exchange of isotopes and an ultimate reduction of the radioactive matter to a very small volume. The following significant aspects are considered:

(a) Difi icultly soluble salts of various systems can be prepared in microcrystalline form and fixed in a fine three-dimensional distribution (impregnation).

(b) Whereas the isotopic exchange has previously been carried out in a batch process, it can be conducted as a column process whereby the dynamic eifects tending to establish an equilibrium are so changed that a complete isotopic exchange can be effected within very short time.

(c) A fixation of ditficultly soluble crystals on cellulose wadding as an inert support (impregnation) enables a high flow rate in the loose structure. Besides, the cellulose wadding laden with the exchanged radioactive ions can be converted into ash except for a small residue.

. (d) The wadding which is impregnated with the difiicultly soluble salts can be stored and does not lose its exchange capacity and may be used without need for preceding chemical operations such as precipitation or the like.

(e) The impregnated wadding has a high exchange capacity so that it can be used in a column process for decontaminating large amounts of liquid.

(f) When wadding consisting of cellulose esters is used, such as collodion wool orcellulose acetate, the support which has been laden with radioactive salts can be dis-' solved in organic solvents, such as methyl acetate. The radioactive salts can then be separated from the carrier by filtration.

The preparation and effectiveness of cellulosic supports impregnated with difficultly soluble salts will become apparent from the following examples:

EXAMPLE 1 The precipitation with equirnolar amounts results in a formation of approximately equivalent crystals, which are free of a surplus of cations or anions at their surface. This prevents the formation of a double electrical layer at the crystal-soultion phase boundary; such double electrical layer could result in undesired secondary effects.

EXAMPLE 2 The wadding is impregnated as in Example 1 but YCl .6H 0 and Na HPO are used instead of Sr(NO EXAMPLE 3 The wadding is impregnated as in Example 1 but Sr(NO and YCl .6H O are added at the same time and are precipitated simultaneously with a solution of Na SO and Na HPO EXAMPLE 4 The wadding is impregnated as in Example 1 but AgNO and an NaI solution are used.

4 EXAMPLE 5-DECONTAMINATION 0.5 gram of a cellulose wadding impregnated according to Example 3 was suspended in H 0 and introduced in a column 30 centimeters long and 2.5 centimeters in diameter. The cellulose column had a height of 5 centimeters. A cock and a superimposed frit slab were provided at the lower end of the column. In other experiments, the frit plate in the column was replaced by glass wool so that a high flow rate was obtained.

An Sr-90 stock solution was provided which contained 23 milligrams Sr(NO 100 milliters as a carrier, 0.5 milliliter was pipetted from said stock solution and filled up to 10 milliliters. The activity was measured in a liquid counting tube and amounted to 14678 pulses per 30 seconds as an average of 10 measurements. These 10 milliliters were diluted to 250 milliliters and the diluted solution was passed through the prepared column at a flow rate of about 200 milliliters per minute. Various samples of 10 milliliters each were taken from the effluent and measured. It was found that the activity of the total volume was about 40 pulses per 30 seconds, which is less than 0.3% of the original activity.

The column of cellulose was then removed from the tube and divided into 10 discs 0.5 centimeter thick each. When the activity of each disc was ascertained, it was found that the activity had been retained entirely in the first disc.

What is claimed is:

1. A process of extracting dissolved radioactive ions from a liquid, which comprises passing said liquid through a column and contacting said liquid in said column with microcrystalline, ditficultly soluble salts, which are iso topic with the dissolved radioactive ions and bonded to the surface of a support, to effect an isotopic exchange between said difiicultly soluble salts and said dissolved radioactive ions, said support consists of a loose, bulky material, and said salts being dispersed Within said material.

2. A process as set forth in claim 1, in which said support consists of cellucotton.

3. A process as set forth in claim 1, in which said support is soluble in organic solvents and is dissolved therein after said isotopic exchange has taken place, and the resulting solution containing radioactive salts is filtered to separate said radioactive salts.

4. A process as set forth in claim 3, in which said support consists of a cellulose ester.

5. A process as set forth in claim 3, in which said support consists of a substance selected from the class consisting of cellulose acetate and cellulose nitrate.

6. A process as set forth in claim 1, in which said support is combustible and is burnt after said ion exchange has taken place.

References Cited UNITED STATES PATENTS 3,034,981 5/1962 Poelman et a1. 2-'l0505X 3,238,056 3/1966 Pall et al 210-505X OTHER REFERENCES R. S. Rai et al.: Radiochim. Acta 5, 30, 1966.

SAMIH N. ZAHARNA, Primary Examiner U.S. Cl. X.R. 210-505 

